Explore how to support SSH based remote debugging

[weinand]

If a debug extension wants to support for SSH based remote debugging it can roll its own implementation in the debug adapter of the extension.

We would like to support SSH based remote debugging in a generic way so that the debug extension only needs to support remote debugging and VS Code takes care of the SSH setup and shutdown.

[weinand]

• setting up a SSH tunneling proxy is simple but requires a software install on some platforms. In addition the software (and its cli) differs on the different platforms.
• xplat ssh npm modules exist, e.g. tunnel-ssh

Proposal: based on an ssh npm module build an easy to configure ssh tunnel implementation that is available to all launch configurations (of all types).